Someone has recommended a book about Polyvagal Theory and how it relates to autism and brain plasticity. Reading up on it though it seems that research into it is only in its infancy. More here:

Polyvagal theory - Wikipedia

The polyvagal theory claims that humans have physical reactions, such as cardiac and digestive changes, associated with their facial expressions[1]. Porges argues this theory with observations from both evolutionary biology and neurology.

I’m wondering if anyone here has looked at this and has any insight?

A brief gallop round Google suggests there is a lot of evidence against, published in very respectable journals.

Thanks. Not going to waste my money on the book then.